1. Field of the Invention
The present invention relates to a semiconductor strain sensor such as a semiconductor acceleration sensor having a beam, and a method for producing the same.
2. Description of the Related Art
Japanese Patent Application Laid-Open Publication No. 6-97465 filed by the present applicant discloses a semiconductor acceleration sensor. The method for producing this semiconductor acceleration sensor is as follows. First, a first conductivity type semiconductor substrate having a second conductivity type epitaxial layer in the surface thereof is prepared. A semiconductor substrate that is located right beneath a predetermined region of the second conductivity type epitaxial layer is electrochemically etched from a reverse side thereof to thereby form a groove. Further, a predetermined region of the thinned portion which has been thinned by the formation of the groove is subjected to dry etching from the epitaxial layer side to thereby form isolation grooves. A cantilever beam is formed owing to these isolation grooves.
In the semiconductor acceleration sensor produced by the above-mentioned conventional method, in order to decrease adverse effects such as noise, it is usual to apply a reverse bias voltage to the PN junction between the second conductivity type epitaxial layer having the first conductivity type gauge portion formed therein and the first conductivity type semiconductor substrate.
However, in the semiconductor strain sensor that has been produced using the above-mentioned method, since the PN junction between the second conductivity type epitaxial layer having the first conductivity type gauge region formed therein and the first conductivity type semiconductor substrate is exposed to the relatively stained side surface (etched surface) of the beam portion or mass portion, there is the drawback that the junction leakage current flows inconveniently through this exposed portion of the PN junction. Especially, in a case where the beam portion is formed by dry etching, the side surface of the beam portion that is exposed as a result of etching is in an atomically very disorderly state and hence in a state where the junction leakage current tends to easily flow therethrough. Accordingly, the use of the conventional method results in large fluctuations or variations in the junction leakage current in the interior of the second conductivity type beam portion. For this reason, the potentials at the respective portions in the second conductivity type epitaxial layer that are located in the beam portion fluctuate. This potential fluctuation causes the fluctuation in the potential in the first conductivity gauge portion, or the occurrence of noise in the first conductivity type gauge portion through the leakage resistance or electrostatic capacitance between the second conductivity type epitaxial layer and the first conductivity type gauge portion.